This invention relates to a vertical type vapor-phase growth apparatus suitable for the vapor-phase growth of a compound semiconductor layer of gallium arsenide or a material including gallium arsenide as a main component.
As a method for effecting the vapor-phase growth of a compound semiconductor layer such as gallium arsenide (GaAs), a method utilizing the thermal cracking of trimethyl gallium (TMG) (one kind of organic gallium) and arsine (AsH.sub.3) (hydrogen arsenide) is known. In the carrying out of such growth method, a vertical type vapor-phase growth reactor has recently come to be used in place of a horizontal type, because no greater amount of feed gas is necessary. In the vertical type reactor a feed gas is supplied substantially vertically down onto samples i.e. crystal substrates and, since the direction in which the feed gas is supplied is the same as the direction in which a vapor-phase growth is effected, such vapor-phase growth can be effected with a lesser amount of feed gas. Since in the vertical type reactor a fairly greater spacing is required between the crystal substrate and a gas inlet hole provided above a crystal substrate bearing support, some gas heated in the neighborhood of the substrate ascends, thus producing a convection phenemenon and involving the following problems:
(1) A variation in the thickness of a growth layer occurs, because a uniform flow of gas in the reactor is prevented; PA1 (2) Some spent gas is reversely flowed toward the upstream portion of the reactor to cause contamination of the feed gas. PA1 (3) The thermal cracking of the fresh feed gas occurs by some heated gas flowed to the upper portion of the reactor, yielding products other than a desired gallium arsenide. As a result, the rate of growth of the vapor-phase growth layer is slowed down.
If such convection occurs within the reactor, the uniformity of the thickness of the growth layer is impeded and, moreover, the layer is formed only at a slower rate of a growth and in lower purity. The effects of the convection are prominently observed as the inner diameter of the reactor is increased, and it has been customary in the prior art to use a reactor having an inner diameter of about 6 cm. For this reason, it is impossible to form a number of growth layers one at a time and thus good productivity, i.e. the theoretical feature of a thermal-cracking vapor-phase growth method can not be expected in the conventional vertical type reactor.